Current trends in internal combustion engine development are towards the use of multi-valve engines capable of operating at higher speeds with higher fuel economy, better engine efficiency, and lower emission levels. The speed-limiting assemblies in an engine are the valve train and the piston assembly. Valve train instability limits engine speed since component breakage and excessive wear will occur in the valve train if it is operated in an unstable mode. For a particular valve train design, the weight of components in the valve train is a major cause of this instability. The heaviest moving part in the valve train is the valve itself.
It is thus desirable to reduce the weight of the valve. In addition to increasing valve train stability, this reduces the amount of engine power used to drive the valve train, and improves fuel consumption. Another advantage of reducing valve weight is that it enables the use of more aggressive cam profiles to open valves earlier and close them later than in conventional practice. This improves volumetric efficiency, and hence increases engine power.
Still further, gains in fuel economy can be realized by proportionately reducing valve spring loads which are designed to control valve motion. The dynamic stresses resulting from valve seat loading are proportional to valve weight, and consequently lower contact stresses from light weight valves will reduce the wear of the seat insert material.
The current approach to lighter weight valves is to reduce valve mass by using narrower stems, or a hollow stem, and to remove material from the valve head. It is estimated that the use of an iron aluminum alloy will realize a weight savings equivalent to that obtained by the use of a hollow valve stem, made from a standard SAE 1541 steel intake valve material.